1. Field of the Invention
The present invention is related to an image reading apparatus for optically reading an image illustrated on an original to be read out from this original, for example, a copying machine and a scanner apparatus.
2. Description of the Related Art
In general, various sorts of image reading apparatus capable of reading color images as well as black/white (monochrome) images have been widely available. Generally speaking, while such a image reading apparatus owns a three-line structure of solid-state image sensing device arrays corresponding to respective color components of R(red), G(green), B(blue) colors in order to read out a color image, when a black/white image is read out, the image reading apparatus produces black/white image data based upon any one of these three R,G,B color component signals. Otherwise, this image reading apparatus acquires a luminance signal “L” by performing the CIE Lab conversion and the like as to the respective R,G,B color component signals so as to produce black/white image data.
However, while the above-described image reading apparatus owns such a merit that the black/white image data can be obtained without requiring the solid-state image sensing device array which is exclusively used to image such a black/white image, this image reading apparatus has such a difficulty. That is, in order to acquire this black/white image data, the respective R,G,B color component signals should be read. Moreover, a predetermined image processing operation (Lab conversion etc.) is required. The high-speed image reading operation can be hardly realized. In particular, while black/white images are read by such image reading apparatus, high-speed reading characteristics thereof are required, as compared with reading operation of color information which requires high gradation characteristics.
Under such a circumstance, very recently, several image reading apparatus have been proposed, which own both the high gradation characteristics realized when color information is read out, and the high-speed characteristics realized when black/white images are read out. For instance, in such an image reading apparatus disclosed in JP-A-Hei. 11-27452, since one line of a solid-state image sensing device array is provided in order to exclusively image a black/white image in addition to a three-line structure of solid-state image sensing device arrays corresponding to the respective R,G,B color components, both the high gradation characteristic and the high-speed characteristic can be realized. Also, as to the solid-state image sensing device array dedicated to the black/white imaging operation, more high-speed operations have been proposed by increasing a total number of transfer registers which are coupled to this solid-state image sensing device array (for instance, normally, while 4 pieces of transfer registers per 1 line are employed instead of 2 pieces thereof, 4-divisional transfer operation is available only for black/white imaging line).
However, in the case that a solid-state image sensing device array exclusively used to image a black/white (monochrome) image is provided, a shift (gap) will be produced at a position to be read on an original, while this shift, or gap corresponds to an interval between this solid-state image sensing device array for imaging the black/white image and solid-state image sensing device arrays for reading a color image. In particular, such a case that transfer registers used for the solid-state image sensing device array exclusively used to image the black/white image is increased, since the interval between the solid-state image sensing device array exclusively used to image the black/white image and the solid-state image sensing device arrays used to image the color image is widened by the space for these increased transfer registers. As a result, the gap of the position to be read on the original is also increased.
Such a gap on the position to be read on the original may introduce a difference in original reading areas between the solid-state image sensing device array exclusively used to image the black/white image, and the solid-state image sensing device arrays used to image the color image. As a consequence, when this gap is increased, there is a risk that a slight cut may be produced in a tip portion of an image read out from an original. Also, there is another risk that noise components produced by reading any positions other than an original (otherwise, platen glass) are superimposed on a reading result of an image.
To avoid this risk, for instance, while a FIFO (First-In First-Out) memory is employed, output timing of image read out results may be delayed in the unit of a line. In an actual case, as to three lines in solid-state image sensing device arrays for imaging a color image, normally, the respective lines are arranged in proximately to each other. As a result, this risk may be solved by performing the line delay process operation with employment of such a FIFO memory. However, since the interval between the solid-state image sensing device array for exclusively imaging the black/white image and the solid-state image sensing device arrays for imaging the color image is made wide, if such a risk is avoided by executing the line delay process operation similar to that of the three lines for the color image, then a very large storage capacity of memories are necessarily required. As a result, there is a certain possibility that the resultant image reading apparatus is manufactured in high cost. Moreover, since the line delay process operation cannot remove the gap itself, this line delay process operation cannot solve the above-explained deterioration in the reading image qualities occurred in the vicinity of the edge portion of the original, which is caused by the large gap.
As a consequence, the present invention has an object to provide an image reading apparatus operable in such a manner that even when a plurality of solid-state image sensing device arrays are arranged to be parallel to each other, a gap of a position to be read on an original, which corresponds to the parallel arrangement of these solid-state image sensing device arrays, can be corrected, so that a deterioration of reading image qualities can be avoided.